Polymers are wildly used in modern day society. In view of such wide spread use, considerable effort has been applied to developing techniques for effectively and efficiently recycling waste polymer.
There are currently well developed techniques for recycling many different types or classes of waste polymer (e.g. polyethylene terephthalate (PET) and polyethylene (PE) that are commonly in the form of containers such as bottles).
Conventional recycling methodology typically involves sourcing waste polymer feedstock. It is not uncommon for that waste feedstock to contain two or more different polymers and potentially non-polymer material.
It is often of critical importance that methodology applied to recycling polymers separates the waste polymer feedstock into different materials to afford polymer streams that are not “contaminated” with different polymer types or non-polymer material. The isolated “clean” polymer stream can then be on sold and processed into a recycled product.
Producing a “clean” polymer stream can be of particular importance because subsequent processing of the polymer into a recycled product can be adversely effected if the polymer contains foreign material such a different polymer or non-polymer material. In particular, each class of polymer (e.g. PET and PE) has a different chemical composition and consequently different properties. These differences typically make polymer mixtures incompatible for being processed together into a recycled product.
Consequently, polymer recycling typically includes methodology for isolating target polymer from mixed waste feedstock. For example, various sensors may be used to assist with bulk sorting the mixed waste feedstock into different classes of polymer. Furthermore, after undergoing such a bulk sorting process, the resulting waste feedstock is typically comminuted and then subjected to further processing to remove any residual contamination. Such further processing is typically categorised as a “wet” or “dry” technique. Float tanks are the most common wet technique in which the comminuted material is separated based on density (i.e. whether it sinks or floats). Cyclone technology is perhaps the most common dry technique used in which the comminuted material is subjected to centrifugal force to separate the material according to weight.
While recycling of waste polymer is now common place, the methodology employed is typically reliant upon the waste polymer feedstock containing target polymer that can be readily physically separated from other components/contaminants in the waste feedstock.
However, many polymer products are produced where the polymer component is bonded to a different substrate material and can not be readily separated and isolated from that substrate material. For example, there is a diverse range of polymer composite structures in which polymer is bonded to a substrate material of different composition. Such polymer composite structures include, for example, laminated polymer composite structures.
While it would be desirable to recycle polymer composite structures in which the polymer is bonded to a different substrate material, conventional recycling methodologies have great difficulty with that task and consequently waste polymer composite structures often end up in landfill.
As a case in point, laminated polyester/polyvinyl chloride composite structures are widely used as trailer side curtains, roll-over tarpaulins, banners, awnings, matting, and general covers. Significant volume of this so called “PVC fabric” is produced annually. While it would be desirable to recycle one or both of the polyester and polyvinyl chloride components of such composite structures, separating and isolating one or both of the polymer components remains problematic. A large volume of such polymer composite structures is therefore diverted to landfill.
An opportunity therefore remains to develop methodology for separating polymer from polymer composite structures to facilitate recycling.